Constitutive Model of Radiation Aging Effects in Filled Silicone Elastomers under Strain

Filled silicone elastomers, an essential component in many technological applications, are often subjected to controlled or unintended radiation for a variety of reasons. Radiation exposure can lead to permanent mechanical and structural changes in the material, which is manifested as altered mechanical response, and in some cases, a permanent set. For unfilled elastomers, network theories developed and refined over decades can explain these effects in terms of chain-scission and cross-link formation and a hypothesis involving independent networks formed at different strain levels of the material. Here, we expose a filled silicone rubber to gamma radiation while being under finite elongational strain and show that the observed mechanical and structural changes can be quantitatively modeled within the same theoretical framework developed for unfilled elastomers as long as nuances associated with the Mullins effect are accounted for in a consistent manner. In this work, we employ Ogden's incompressible hyperelastic model within the framework of Tobolsky's two-network scheme to describe the observed permanent set and mechanical modulus changes as a function of radiation dosage. In the process, we conclude that gamma radiation induces both direct cross-linking at chain crossings (H-links) and main-chain-scission followed by cross-linking (Y-links). We provide an estimate of the ratio of chain-scission to cross-linking rates, which is in reasonable agreement with previous experimental estimate from Charlesby-Pinner analysis. We use density functional theory (DFT)-based quantum mechanical calculations to explore the stability of -Si and -SiO radicals that form upon a radiation-induced chain-scission event, which sheds light on the relative rates of Y-linking and H-linking processes.

Age-aware constitutive materials model for a 3D printed polymeric foam

Traditional open or closed-cell stochastic elastomeric foams have wide-ranging applications in numerous industries: from thermal insulation, shock absorbing/gap-filling support cushions, packaging, to light-weight structural and positional components. Recent developments in 3D printing technologies by direct ink-write have opened the possibility of replacing stochastic foam parts by more controlled printed micro-structures with superior stress-distribution and longer functional life. For successful deployment as mechanical support or structural components, it is crucial to characterize the response of such printed materials to long-term external loads in terms of stress-strain behavior evolution and in terms of irreversible structural and load-bearing capacity changes over time. To this end, here we report a thermal-age-aware constitutive model for a 3D printed close-packed foam structure under compression. The model is based on the Ogden hyperfoam strain-energy functional within the framework of Tobolsky two-network scheme. It accurately describes experimentally measured stress-strain response, compression set, and load retention for various aging times and temperatures. Through the technique of time-temperature-superposition the model enables the prediction of long-term changes along with the quantification of uncertainty stemming from sample-to-sample variation and measurement noise. All aging parameters appear to possess the same Arrhenius activation barrier, which suggests a single dominant aging mechanism at the molecular/network level.

What is Diverse Enough? How "Intentionally Diverse" Charter Schools Recruit and Retain Students

School choice has the potential to be a tool for desegregation, but research suggests that choice more often exacerbates segregation than remedies it. In the past several years, hundreds of 'intentionally diverse' charter schools have opened across the country, potentially countering the link between charter schools and segregation. Yet, these schools raise important questions about choice, segregation, and equity. For instance: how do leaders of diverse charter schools prioritize diversity in decisions about location, marketing, and recruitment? What are the implications of these diversity efforts for equity, especially within competitive and marketized educational contexts? We explore the concrete recruiting and marketing strategies schools used to build and retain their diverse communities, drawing on qualitative data from New Orleans, LA and Minneapolis-St. Paul, MN. We identify key strategies used by school leaders, but also note that many strategies were ad-hoc and experimental. Furthermore, we note that schools often did not articulate their goals for diversity, making them susceptible to external pressures that might refocus attention away from equity and diversity, or allow groups with more power to shape agendas within the school. Finally, we find that gentrification and widening economic inequities threatened schools' efforts to recruit and maintain a diverse student body. We discuss implications for leaders of diverse charter schools and other leaders seeking to diversify their student bodies, as well as policymakers and charter authorizers.

Age and factors associated with self-clean intermittent catheterization in patients with spina bifida

PURPOSE

The purpose of this study is twofold: 1) to determine the age when a child with spina bifida (SB) will most likely transition from caregiver clean intermittent catheterization (CIC) to self-CIC, and 2) to identify factors associated with self-CIC in children older than that age.

METHODS

This is a retrospective, single-institution cohort study of individuals with SB. Data were collected prospectively as part of the National Spina Bifida Patient Registry. For Aim 1, we identified all individuals who perform self-CIC and who had a documented transition from caregiver-CIC. We then determined the age of transition to self-CIC. For Aim 2, we compared individuals over age 10 years (age cutoff determined by Aim 1) who use self-CIC to those who use caregiver-CIC to determine what variables were associated with self-CIC.

RESULTS

From our SB population, 206 individuals used self-CIC. Of these, 64 patients had documented ages of transition from caregiver- to self-CIC. 46 (71.9%) and 56 (87.5%) patients had transitioned to self-CIC by 10 and 14 years, respectively. For Aim 2, we used age 10 as a cutoff, based on the findings from Aim 1, and found that 287/696 patients were ⩾ 10 years and using CIC. Factors independently associated with lower likelihood of self-CIC were thoracic spinal lesions (odds ratio (OR) 0.45) and Medicaid insurance (OR 0.24).

CONCLUSIONS

The ages at self-CIC transition vary, although most patients transition by age 10. Thoracic-level spinal lesions and Medicaid insurance are associated with lower odds of self-CIC.

Mullins effect in a filled elastomer under uniaxial tension

Modulus softening and permanent set in filled polymeric materials due to cyclic loading and unloading, commonly known as the Mullins effect, can have a significant impact on their use as support cushions. A quantitative analysis of such behavior is essential to ensure the effectiveness of such materials in long-term deployment. In this work we combine existing ideas of filler-induced modulus enhancement, strain amplification, and irreversible deformation within a simple non-Gaussian constitutive model to quantitatively interpret recent measurements on a relevant PDMS-based elastomeric cushion. We find that the experimental stress-strain data is consistent with the picture that during stretching (loading) two effects take place simultaneously: (1) the physical constraints (entanglements) initially present in the polymer network get disentangled, thus leading to a gradual decrease in the effective cross-link density, and (2) the effective filler volume fraction gradually decreases with increasing strain due to the irreversible pulling out of an initially occluded volume of the soft polymer domain.

Post-Polymerization Crosslinked Polyurethane Shape-Memory Polymers

Novel urethane shape-memory polymers (SMPs) of significant industrial relevance have been synthesized and characterized. Chemically crosslinked SMPs have traditionally been made in a one-step polymerization of monomers and crosslinking agents. However, these new post-polymerization crosslinked SMPs can be processed into complex shapes by thermoplastic manufacturing methods and later crosslinked by heat exposure or by electron beam irradiation. Several series of linear, olefinic urethane polymers were made from 2-butene-1,4-diol, other saturated diols, and various aliphatic diisocyanates. These thermoplastics were melt-processed into desired geometries and thermally crosslinked at 200°C or radiation crosslinked at 50 kGy. The SMPs were characterized by solvent swelling and extraction, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile testing, and qualitative shape-recovery analysis. Swelling and DMA results provided concrete evidence of chemical crosslinking, and further characterization revealed that the urethanes had outstanding mechanical properties. Key properties include tailorable transitions between 25 and 80°C, tailorable rubbery moduli between 0.2 and 4.2 MPa, recoverable strains approaching 100%, failure strains of over 500% at T(g), and qualitative shape-recovery times of less than 12 seconds at body temperature (37°C). Because of its outstanding thermo-mechanical properties, one polyurethane was selected for implementation in the design of a complex medical device. These post-polymerization crosslinked urethane SMPs are an industrially relevant class of highly processable shape-memory materials.

Embolectomy in a rabbit acute arterial occlusion model using a novel electromechanical extraction device

A prototype endovascular electromechanical clot-extraction device was fabricated using a combination of shape memory polymer and shape memory nickel-titanium alloy (nitinol). Five embolic vascular occlusions were created in 4 rabbits by injecting thermally coagulated blood through a 4F catheter in the common carotid artery. Angiography immediately after clot injection showed complete or partial occlusion of the common carotid artery. Posttreatment angiography showed complete (2/5), partial (2/5), or no (1/5) restoration of blood flow.

Age-related changes in levels of tyrosine kinase B receptor and fibroblast growth factor receptor 2 in the rat inferior colliculus: implications for neural senescence

Brain-derived neurotrophic factor and fibroblast growth factor 2, and their respective binding sites, tyrosine kinase B receptor and fibroblast growth factor receptor 2, are known to regulate neurite outgrowth and antioxidant enzyme activity. Several studies suggest that brain-derived neurotrophic factor and fibroblast growth factor are contained in the inferior colliculus. Previous work in our laboratories revealed dendritic and synaptic losses in the inferior colliculus of aged Fischer-344 rats, along with coincident increases in lipid peroxidation possibly linked to a decrease in activity of antioxidant enzymes. In an effort to identify potential causal mechanisms underlying age-related synaptic and dendritic losses that occur in the inferior colliculus, the present study attempted to determine if inferior colliculus levels of tyrosine kinase B receptor and fibroblast growth factor receptor 2 expression are altered with age. Immunocytochemistry was performed in the inferior colliculus, hippocampus and cerebellum of 3-month-old F344 rats to study distributions of the full-length and truncated isoforms of tyrosine kinase B receptor, and fibroblast growth factor receptor 2. The latter two brain regions served as positive controls. For all three antigens, immunolabeling was localized primarily in somata and proximal dendrites in all subdivisions of the inferior colliculus, and in the dentate gyrus and Ammon's horn of the hippocampus. In the cerebellum, the somata and dendrites of the Purkinje cells were also immunolabeled.A significant reduction in levels of the full-length form of tyrosine kinase B receptor in 18- and 25-month-old rats (respectively, approximately 20% and 30% relative to 3-month-olds) was revealed using western blot analyses. Inferior colliculus and hippocampal levels of the truncated form were modestly decreased ( approximately 7%) as well in the two older age groups. In contrast, levels of fibroblast growth factor receptor 2 in the inferior colliculus and hippocampus were elevated by approximately 35% in the two older age groups when compared to 3-month-olds. Changes in cerebellar levels of tyrosine kinase B receptor and fibroblast growth factor receptor 2, while similar to those in the inferior colliculus and hippocampus among the age groups, did not achieve statistical significance in this study. These findings give rise to the possibility that age-related reductions in tyrosine kinase B receptor levels could be a causal factor in the degenerative changes observed in the inferior colliculus of aged animals, including mitochondrial damage and dendritic regression. The observed increases in fibroblast growth factor receptor 2 levels may be compensatory to the increased oxidative stress. The effectiveness of the fibroblast growth factor receptor 2 response is questionable given the damage that occurs in the inferior colliculus and hippocampus of aged animals. However, the deficits could worsen in the absence of an increase in fibroblast growth factor receptor 2.

LASIK surgery

The laser in situ keratomileusis (i.e., LASIK) procedure reshapes the surface of the cornea to focus visual images directly onto the retina, thereby improving visual acuity. In 1998, approximately 420,000 LASIK procedures were performed in the United States, and approximately two million people throughout the world already are benefiting from the LASIK vision correction procedure.

The need for more physicians trained in abortion: raising future physicians' awareness

A woman presents to her physician with a newly diagnosed condition that in her considered and informed judgment requires an elective surgical procedure. The physician, after speaking with her, agrees that this is an acceptable option. The procedure in question is in fact one of the commonest surgeries performed on American women. The physician is also aware that although the procedure is deemed elective in this and in most cases, research has shown that the consequences of not providing the procedure when it is requested can be severe in terms of both physical and emotional sequelae—in fact, the woman's death can be a worst-case result when the procedure is denied. However, this senior physician is also aware that the procedure is controversial, and that ever fewer of his (now mostly younger) colleagues perform it, either because they are not appropriately trained, not so inclined, or fearful of becoming the target of vocal and even violent opponents of the procedure. In fact, he knew of seven American physician colleagues who had been slain in the past five years for providing this procedure, and of 16 more attempted slayings. Seeking an appropriate referral for this patient, the physician learns that she will have to travel hundreds of miles, involving considerable additional expense and delay—which itself can add to the complexity and risk of the procedure. Presented with this option, the patient expresses dismay but also her resigned commitment to follow through with this referral, and leaves the office in tears.

An outbreak of Salmonella enteritidis phage type 4 infection in a rural community in Northern Ireland

An outbreak of gastroenteritis arose in people who attended a charity barbecue at a hotel in a rural area of Northern Ireland in July 1995. About 120 people attended the barbecue, 98 of whom were identified. Fifty-one of them and seven members of hotel staff met the case definition. An epidemiological investigation showed that illness was significantly associated with eating foods containing mayonnaise that had been prepared using raw shell eggs and stored at too high a temperature. Salmonella enteritidis phage type 4 was cultured from 17 out of 24 faecal specimens received from people who attended the barbecue and in 17 out of 34 faecal specimens from staff, including all seven staff cases. The primary source of infection was not identified despite thorough investigation. This paper highlights the value of administering questionnaires by telephone when investigating community outbreaks of infection in rural areas, the important role of general practitioners in the identification of community outbreaks, and the need to periodically reiterate public health messages, in particular for food handlers and caterers.

Salmonella in retail poultry in Northern Ireland

A prospective survey was carried out in Northern Ireland between February and August 1994 to assess the current levels of salmonella in retail chickens, and to determine whether contamination rates differed between chickens sold in supermarkets and by butchers. One hundred and forty chilled and frozen raw chickens were sampled from retail display and examined for the presence of salmonella using an approved method. Contamination was commoner in chickens that were chilled, sold from smaller premises, and reared or slaughtered outside Northern Ireland. Salmonella enteritidis phage type 4 was the most commonly isolated type. The contamination rate of about 7% is considerably lower than in Great Britain and this may partially explain the lower rate of human salmonella infections in Northern Ireland. This finding supports the recommendations made in the Advisory Committee on the Microbiological Standards of Food's report on poultry meat, since many of the improvements proposed are already in operation in areas of the Northern Ireland poultry industry.

Assessment of skeletal muscle viability by PET

We investigated the use of [18F]fluoro-2-deoxyglucose (FDG) PET scanning for assessment of skeletal muscle viability in patients with peripheral vascular disease and in patients following free-flap skeletal muscle transfer for closure of open wounds.

METHODS

We obtained 32 FDG-PET scans from 30 patients, either at the time of admission for peripheral vascular disease (n = 16) or between 1 and 15 days after surgery for skeletal muscle transfer (n = 16). Ratios between injured and contralateral limb FDG tracer activity uptake were correlated with clinical outcome at 1 mo to 3 yr follow-up.

RESULTS

Viable muscle uptake ratios ranged from 0.47 to 7.88 (mean: 2.26 +/- 1.81; n = 26), while nonviable muscle uptake ratios ranged from 0.12 to 0.46 (mean: 0.27 +/- 0.12; n = 6; p < 0.02). After skeletal muscle transfer, two patients with viable tissue, as documented by PET, required amputation due to osteomyelitis, and one patient with peripheral vascular disease who showed viable tissue by PET required amputation 3 mo after the PET scan because of recurrent ulcers.

CONCLUSION

FDG-PET scanning can determine skeletal muscle viability in patients with peripheral vascular disease and in patients following free-flap transfer.

Investigation of a nosocomial outbreak of Pseudomonas aeruginosa pneumonia in an intensive care unit by random amplification of polymorphic DNA assay

From July to September 1993 in the intensive care unit of the Royal Victoria Hospital there were 10 cases of pneumonia associated with sputum culture of Pseudomonas aeruginosa. The isolates had an identical biotype and pyocine typing profile. The same strain of P. aeruginosa was recovered from the sink plug-hole in two rooms, and the tap handles and ventilator tubing in a third room. All strains were retrospectively typed by the random amplification of polymorphic DNA (RAPD) method using a 26-mer oligonucleotide primer, and were identical in profile. Recommendations to medical and nursing staff included secretion isolation precautions, terminal disinfection after patient discharge, use of disposable vinyl gloves by hospital staff for all body substance contacts, thorough handwashing with 4% chlorhexidine gluconate before and after dealing with all patient contacts, and prompt, appropriate antibiotic treatment for P. aeruginosa pneumonia. RAPD is a simple and effective method to determine the relatedness of P. aeruginosa isolates, and typing results are available within a single working day; thus dramatically increasing its clinical relevance over existing molecular methods.

The effects of HIV/AIDS intervention groups for high-risk women in urban clinics

OBJECTIVE

This study reports the results of a behavior change intervention offered to women at high risk for human immunodeficiency virus (HIV) infection seen in an urban primary health care clinic.

METHODS

Participants were 197 women randomly assigned to either an HIV/acquired immunodeficiency syndrome (AIDS) risk reduction group or a comparison group. Women in the HIV/AIDS intervention group attended five group sessions focusing on risk education; skills training in condom use, sexual assertiveness, problem solving, and risk trigger self-management; and peer support for change efforts. Women in the comparison group attended sessions on health topics unrelated to AIDS.

RESULTS

At the 3-month follow-up, women in the HIV/AIDS intervention group had increased in sexual communication and negotiation skills. Unprotected sexual intercourse had declined significantly and condom use had increased from 26% to 56% of all intercourse occasions. Women in the comparison group showed no change.

CONCLUSIONS

Socially disadvantaged women can be assisted in reducing their risk of contracting HIV infection. Risk reduction behavior change interventions should be offered routinely in primary health care clinics serving low-income and high-risk patients.

Immunoglobulin G (IgG) serological response to Branhamella catarrhalis in patients with acute bronchopulmonary infections

Over 12 months serum was collected from 45 inpatients, with acute bronchopulmonary infection, in whose sputum Branhamella catarrhalis predominated, or was the sole pathogen. Serum was examined for IgG against B catarrhalis using an immunofluorescence antibody test. Acute and convalescent sera were compared with sera of age and sex matched controls. The convalescent sera had significantly higher titres than the acute sera which in turn had higher titres than the controls. The findings confirm the role of B catarrhalis as a respiratory pathogen and suggest that patients with chronic pulmonary disease are more prone to infection with this organism than the general population.

Outbreak of Legionnaires' disease in Glasgow Royal Infirmary: microbiological aspects

The bacteriological investigation of an outbreak of Legionnaires' disease in Glasgow Royal Infirmary affecting 16 patients is described. Most of the patients had been treated in high-dependency areas on two floors of the hospital supplied by the same two air-conditioned ventilation systems. The source of infection was traced to contamination of a cooling tower from which a plume of spray discharged into the intake vents of the two ventilation systems. Rubber grommets within the cooling tower probably provided a nidus of infection there. The control and management of the outbreak are discussed: a policy of frankness about the course and progress of the investigations was adopted and helped to allay anxiety on the part of both staff and media.

Dietary copper intake in artificially fed infants

Plasma concentrations of copper and zinc and leucocyte concentrations of zinc were measured in mothers during later pregnancy, at delivery, and 8-10 weeks after birth, and plasma concentrations of copper and zinc were measured in their infants at delivery and 8-10 weeks after birth. The 145 infants were either breast fed or fed one of two milk formulas supplying copper at different concentrations. None of the infants achieved the minimum copper intakes recommended by the World Health Organisation (WHO). At 2 months of age there were no major differences in growth or health detected in infants fed the different copper intakes. Infant birth weight correlated well with the ratio of maternal venous plasma zinc:maternal leucocyte zinc at delivery. Maternal venous plasma copper and zinc concentrations at birth correlated with umbilical venous plasma copper and zinc concentrations. Infants fed the higher copper content formulas had a low mean plasma zinc concentration without a significant increase in the mean plasma copper concentration. The present WHO recommendations regarding minimum copper intakes for infants fed formulas cannot be achieved with currently available formulas and are probably wrong.

Immunohistochemical studies of keratin in human bronchus and lung tumors

Lung tumors of various types, fixed in 4% formaldehyde-1% glutaraldehyde, were stained for keratin proteins. The results were compared with previous ultrastructural evidence of intermediate filament bundles (IFBs), presumed to be keratin. Electron and light microscopic methods were largely complimentary and the results were in agreement in 79% of cases. Light microscopy was superior for demonstrating keratinizing foci containing numerous well-developed IFBs, whereas electron microscopy was superior when keratin filaments were sparsely distributed in cells throughout a tumor. Fetal and adult bronchial specimens were also studied. Normal adult bronchus, fixed in aldehydes, was unreactive but keratin was observed in similarly fixed bronchi that showed epidermoid metaplasia and/or intraepithelial carcinoma. Keratin was demonstrated in normal adult bronchi fixed in ethanol. Keratin was not observed in fetal lung until the 14th week of gestation, when it appeared in basal cells and a few columnar cells of the larger bronchi. Thereafter, keratin progressively appeared in the more distal branches. As specimens from gestations of less than 14 weeks were fixed in aldehydes, the apparent lack of immunoreactivity may have been artifactual. Nevertheless, keratin was demonstrable in aldehyde-fixed fetal bronchi at 16 and 23 weeks' gestation.

Histochemical studies of dense-core granulated tumors of the lung. Neuron-specific enolase as a marker for granulated cells

It is well known that carcinoid tumors and some small-cell carcinomas of the lung contain dense-core granules (DCGs). Moreover, a small number of tumors presenting with epidermoid, large-cell, or adenocarcinoma histologic characteristics (so-called atypical endocrine tumors), also contain DCGs. Herein, we describe certain histochemical features of DCG tumors and compare them with other major lung tumor types that lack DCGs (non-DCG tumors). All DCG tumors contained neuron-specific enolase and many contained serotonin. These markers were not present in any non-DCG tumor. Other histochemical markers (glycogen, mucosubstances, corticotropin, beta-human chorionic gonadotropin, keratin, somatostatin, and calcitonin) were found in a proportion of DCG and non-DCG tumors, but were, in general, more common in non-DCG tumors and atypical endocrine tumors than in carcinoids and small-cell carcinomas. alpha-Fetoprotein was rarely found in non-DCG tumors, and was never observed in DCG tumors. The atypical endocrine group represents a class of tumors with a remarkably mixed and varied phenotype. Their potential significance is discussed and methods to facilitate their diagnosis are suggested.

Rubella: immunity and vaccination in schoolgirls

Of 191 schoolgirls, 128 volunteered to take part in a feasibility study of serotesting before and after rubella vaccination, and all responded to RA 27/3 vaccine. Had the serum samples been taken by a fingerprick method the number of volunteers would probably have increased considerably. A change in policy for rubella vaccination to testing both before and after vaccination would cost no more than the existing policy, would ensure primary response, and would differentiate those women who were protected by the vaccine from those with antibody to wild virus.

Reduction in exposure to lead from drinking water and its effect on blood lead concentrations

The water supply in Ayr (Scotland, UK) was plumbosolvent and many dwellings in Ayr contained lead pipes. In 1981 treatment of the water supply to reduce its plumbosolvency was initiated. Measurements of water and blood lead concentrations were made before and subsequent to the treatment. Most of the measurements made before and after water treatment began were made on water samples from the same dwellings and blood samples from the same women. Water treatment produced a sharp fall in water lead concentrations and a decrease in the median blood lead concentration from 21 to 13 micrograms/100 ml. Two women had higher than expected blood lead concentrations, both these women had been removing old paint. Women who had lead pipes removed from their dwellings all showed substantial decreases in their blood lead concentrations. The curvilinearity of the relation between blood lead and water lead concentrations is confirmed. Even relatively low (less than 40 micrograms/l) water lead concentrations may make a substantial contribution to blood lead concentrations.

Keratin proteins in human lung carcinomas. Combined use of morphology, keratin immunocytochemistry, and keratin immunoprecipitation

Light-microscopic immunocytochemistry and electron microscopy demonstrated that adenocarcinomas (AC) and squamous cell (epidermoid) carcinomas (SCCs) of human lung contained keratin proteins in the form of tonofilament bundles. However, moderately differentiated (md) SCCs contained abundant keratin, whereas poorly differentiated (pd) SCCs and all ACs contained lesser amounts. Lung tumors with the diagnosis of AC or SCC, as defined by WHO criteria, were also analyzed by immunoprecipitation techniques for the presence of keratin proteins. Regardless of the degree of tumor differentiation, SCCs contained a 44 kd keratin which was lacking in ACs. Interestingly, normal bronchial epithelium also contained the same 44 kd keratin. In addition, as SCCs became more differentiated, they exhibited even greater differences in the profile of synthesized keratins. Specifically, the relative abundance of the intermediate-sized keratins (57 and 59 kd) was increased in the md SCCs. Although keratin protein patterns appear to be a valuable adjunct in distinguishing AC from SCC, their usefulness as a diagnostic tool will require survey of a larger number of poorly differentiated tumors.

Regeneration of hamster tracheal epithelium after mechanical injury. IV. Histochemical, immunocytochemical and ultrastructural studies

All stages of regeneration in hamster tracheal epithelium were studied following a denuding mechanical injury. At 1 h all the cells had sloughed from the wound site leaving a bare and sometimes disrupted basal lamina. Viable cells at the wound margins rapidly changed shape, flattened and migrated to cover the denuded lesion by 12 h. In addition, epithelial cells that remained viable demonstrated sublethal changes that included the rapid discharge of mucous granules from secretory cells, internalization of cilia by ciliated cells and evidence of heterophagy in both cell types. By 24 h a wave of epithelial cell divisions occurred, primarily by secretory cells. This produced a multilayered epidermoid metaplasia that was best developed at 48 h. The metaplastic epithelium was largely composed of cells with both secretory (mucous granules) and epidermoid (tonofilament bundles and numerous desmosomes) characteristics. The peroxidase-antiperoxidase (PAP) method demonstrated a few keratin-positive cells in the wound as early as 12 h post-wounding and keratin was demonstrated in more cells by 24 h. All cells in the metaplastic wound epithelium were keratin-positive by 48 h. Following 48 h some of the most superficial keratinized cells sloughed from the epithelium and the keratin content of the remaining cells began to decline. At 72 h pre-ciliated and pre-secretory cells were seen in the wound. Pre-ciliated cells were characterized by an abundant electron-lucent cytoplasm, large pale nucleus, filiform apical microvilli and evidence of ciliogenesis, similar to that seen during fetal development. Pre-ciliated cells often contained apical mucous granules, apparently carried over from the parent secretory cells. With the appearance of these columnar cells the normal mucociliary morphology was restored in small wounds by 120 h, but some persistent epidermoid metaplasia remained in the large wounds through 168 h post-wounding. These data provide further evidence for the important role of secretory cells in the histogenesis of epidermoid metaplasia and the regeneration of normal morphology following injury. The implications of these findings in understanding the histogenesis of other lesions in the tracheo-bronchial epithelium are discussed.

An Alcian blue (pH 2.5)-PAS-keratin immunoperoxidase method for the simultaneous demonstration of keratin and neutral and acidic mucosubstances

A method is proposed for the simultaneous staining of neutral and acidic, periodate reactive and nonperiodate reactive mucosubstances, glycogen and keratin in paraffin sections. Briefly, sections are stained by the Alcian blue (pH 2.5)-PAS method, followed by a peroxidase-antiperoxidase immunohistochemical stain for keratin. The proposed method modifies an existing method, and expands the range of polysaccharides and mucosubstances which may be demonstrated. The proposed method is easily performed within a single working day and promises to be of value in surgical pathology as well as in studies of bronchial carcinogenesis.

Assessment of lead intakes and dose-response for a population in Ayr exposed to a plumbosolvent water supply

1 Dietary lead intakes, blood lead concentrations and water lead concentrations were measured and their relationships investigated for 31 adults and 11 infants living in dwellings in Ayr with lead plumbing. 2 For adults, some lead intakes were found to be higher than the provisional tolerable weekly intake for lead, and for infants most of the intakes were high. 3 A cube root relationship fitted the data on blood lead versus water lead better than a linear relationship. Similarly, blood lead varied with the cube root of weekly dietary lead intake. 4 These cube root equations provided a means of estimating the impact on blood lead concentrations of exposure to lead from food and water. If cube root relationships correctly describe the association between these parameters, then the curve fitted to the results for adults indicates that the contribution to the blood lead concentrations from sources other than the diet and water was relatively small.

Elaboration of human chorionic gonadotropin by lung tumors: an immunocytochemical study

The highly sensitive peroxidase-antiperoxidase immunocytochemical method was used to demonstrate the presence of the beta-subunit of human chorionic gonadotropin (HCG) within paraffin sections of human lung tumors of diverse histologic patterns. Of the 61 tumors studied, 51 (84%) displayed HCG-like immunoreactivity. This is a much higher incidence than was expected considering studies by other investigators in which serum samples from patients with lung cancer were assayed for HCG. Our results are, however, consistent with data from studies by other investigators in which tumor extracts were assayed for HCG. In addition, it was found that HCG production was often linked with glycogen storage within tumor cells. This may explain the association of HCG production with large-cell carcinomas of the lung, because these tumors often contain copious quantities of glycogen.

Atypical endocrine tumors of the lung

Seven malignant peripheral lung tumors that were diagnosed using light microscopy as large-cell carcinomas or as epidermoid or adenocarcinomas were studied by light and electron microscopic histochemistry. All tumors contained numerous dense-core granules. The cells were joined by desmosomes and contained well-developed tonofilament bundles. Serotonin was demonstrated in six of seven tumors and argyrophilic granules were demonstrated in five of six tumors tested. Four tumors produced mucus. All tumors extended to the visceral pleura and two invaded the chest wall. The existence of lung tumors that contain serotonin and bear argyrophilic putative endocrine granules, but that do not have a light-microscopic histology characteristic of either carcinoid or oat-cell carcinomas, is confirmed. The presumptive endocrine nature of such tumors usually passes unrecognized because they lack criteria to allow diagnosis by routine methods.

A bacteriological investigation of two leisure centre swimming pools disinfected with ozone

A bacteriological study was carried out on the first Leisure Centre swimming pools in the United Kingdom to be disinfected with ozone/chlorine. Results suggested that a free chlorine concentration of approximately 0.8 mg/l was necessary to maintain the pools in a bacteriologically satisfactory condition. This amount of free chlorine was similar to that required when the pool was disinfected with chlorine alone. However, the associated amount of combined chlorine was much lower when disinfection was by ozone/chlorine and this gave more acceptable bathing conditions. Implications for the manamgement of pools disinfected by this method are discussed.